U.S. patent application number 12/492661 was filed with the patent office on 2009-12-31 for method and system for sterilizing objects by the application of gas-cluster ion-beam technology.
This patent application is currently assigned to EXOGENESIS CORPORATION. Invention is credited to Sean R. Kirkpatrick, Richard C. Svrluga.
Application Number | 20090321658 12/492661 |
Document ID | / |
Family ID | 41445341 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090321658 |
Kind Code |
A1 |
Kirkpatrick; Sean R. ; et
al. |
December 31, 2009 |
METHOD AND SYSTEM FOR STERILIZING OBJECTS BY THE APPLICATION OF
GAS-CLUSTER ION-BEAM TECHNOLOGY
Abstract
Methods and systems for sterilization of objects by gas-cluster
ion-beam (GCIB) irradiation are disclosed. The sterilization may be
in conjunction with other beneficial GCIB surface processing of the
objects. The objects may be medical devices or surgically
implantable medical prostheses.
Inventors: |
Kirkpatrick; Sean R.;
(Littleton, MA) ; Svrluga; Richard C.; (Newton,
MA) |
Correspondence
Address: |
BURNS & LEVINSON, LLP
125 SUMMER STREET
BOSTON
MA
02110
US
|
Assignee: |
EXOGENESIS CORPORATION
Wellesley Hills
MA
|
Family ID: |
41445341 |
Appl. No.: |
12/492661 |
Filed: |
June 26, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61075957 |
Jun 26, 2008 |
|
|
|
Current U.S.
Class: |
250/455.11 |
Current CPC
Class: |
A61L 12/10 20130101;
A61L 2/20 20130101; A61L 2202/24 20130101; H01J 2237/0812 20130101;
A61L 2/087 20130101 |
Class at
Publication: |
250/455.11 |
International
Class: |
A61L 2/08 20060101
A61L002/08 |
Claims
1. A method for sterilizing a workpiece, comprising the steps of:
providing a reduced pressure chamber; forming an accelerated
gas-cluster ion-beam having a path in the reduced pressure chamber;
providing a workpiece holder in the reduced pressure chamber for
holding the workpiece in the accelerated gas-cluster ion-beam path;
and irradiating at least a portion of a surface of the workpiece
with the accelerated gas-cluster ion-beam for sterilizing the
portion.
2. The method of claim 1, wherein the irradiating step introduces a
dose of at least 10.sup.13 ions/cm.sup.2 to the at least a portion
of the surface of the workpiece.
3. The method of claim 1, wherein the forming step includes
accelerating the gas-cluster ion-beam using an acceleration
potential of at least 2 kV.
4. The method of claim 1, wherein the forming step comprises
forming a gas-cluster ion-beam comprising a noble gas or a mixture
of a noble gas with oxygen.
5. The method of claim 1, wherein the at least a portion of a
surface is an entire surface.
6. The method of claim 1, wherein the providing a workpiece holder
step further comprises sterilizing the workpiece holder.
7. A method for sterilizing a workpiece, comprising the steps of:
a. providing a chamber having an interior and a workpiece holder in
the interior; b. initially sterilizing the workpiece holder and the
interior of the chamber; c. forming an accelerated gas-cluster
ion-beam; d. loading a workpiece onto the workpiece holder to be
held thereby for sterilization; e. reducing the pressure in the
chamber; f. directing the accelerated gas-cluster ion-beam onto the
workpiece; g. irradiating at least a portion of a surface of the
workpiece with the accelerated gas-cluster ion-beam; h.
discontinuing irradiation when the at least a portion of a surface
of the workpiece has received a predetermined dose; and i.
unloading the workpiece from the workpiece holder and removing it
from the chamber.
8. The method of claim 7, further comprising the step of: venting
the chamber with a sterile gas.
9. The method of claim 8 further comprising the step of: repeating
steps d. through i. at least once.
10. The method of claim 7, wherein the at least a portion of a
surface is an entire surface.
11. The method of claim 7, wherein the step of unloading includes
placing the workpiece directly into a sterile container.
12. A method for sterilizing a workpiece, comprising the steps of:
providing a chamber having an interior and a workpiece holder;
initially sterilizing the workpiece holder and the interior of the
chamber; loading a workpiece onto the workpiece holder to be held
thereby; forming a first accelerated gas-cluster ion-beam;
directing the first accelerated gas-cluster ion-beam onto the
workpiece; first processing the workpiece by irradiating at least a
first portion of the surface of the workpiece with the first
accelerated gas-cluster ion-beam; discontinuing first processing
when the at least a first portion of the surface of the workpiece
has received a predetermined dose; forming a second accelerated
gas-cluster ion-beam; directing the second accelerated gas-cluster
ion-beam onto the workpiece; second processing the workpiece by
irradiating at least a second portion of the surface of the
workpiece with the second accelerated gas-cluster ion-beam;
discontinuing second processing when the at least a second portion
of the surface of the workpiece has received a predetermined dose;
unloading the workpiece from the workpiece holder and removing it
from the chamber; and wherein either of the first processing step
or the second processing step is a sterilizing step.
13. The method of claim 12 wherein the at least a first portion of
the surface and the at least a second portion of the surface are
the same portion of the surface.
14. An apparatus for sterilizing a workpiece, comprising: a reduced
pressure chamber having an interior; a sterilizer adapted for
initially sterilizing the interior of the reduced pressure chamber;
an apparatus adapted for forming an accelerated gas-cluster
ion-beam having a path in the interior of the reduced pressure
chamber; a workpiece holder adapted for holding a workpiece in the
path of the accelerated gas-cluster ion-beam in the interior of the
reduced pressure chamber for receiving an irradiated gas-cluster
ion-beam dose on at least a portion of the surface of the
workpiece; a vent adapted for venting the reduced pressure chamber
with a sterile gas; and a mechanism adapted for loading and/or
unloading the workpiece onto or off of the holding means in the
reduced pressure chamber and adapted for introducing and/or
removing the workpiece from the reduced pressure chamber.
15. The apparatus of claim 14, wherein the workpiece holder further
comprises means for rotating, articulating, repositioning, or
moving the workpiece to provide for receiving an irradiated
gas-cluster ion-beam dose on multiple portions of the surface of
the workpiece.
16. The apparatus of claim 15, wherein the multiple portions of the
surface the workpiece comprise the entire surface of the
workpiece.
17. The apparatus of claim 14, wherein the apparatus adapted for
forming an accelerated gas-cluster ion-beam further comprise: a
nozzle; a skimmer; an ionizer; and an accelerator.
18. The apparatus of claim 14, further comprising a device adapted
for scanning the accelerated gas-cluster ion-beam.
19. The apparatus of claim 14, wherein the sterilizer adapted for
initially sterilizing the interior of the reduced pressure chamber
comprises means for introducing and removing a sterilant gas
to/from the interior of the reduced pressure chamber.
20. The apparatus of claim 14, wherein the sterilizer adapted for
initially sterilizing the interior of the reduced pressure chamber
comprises means for irradiating the interior of the reduced
pressure chamber with ultraviolet radiation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority from U.S.
Provisional Patent Application No. 61/075,957, filed Jun. 26, 2008,
entitled METHOD AND SYSTEM FOR STERILIZING OBJECTS BY THE
APPLICATION OF GAS CLUSTER ION BEAM TECHNOLOGY, the contents of
which are hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0002] This invention relates generally to the sterilization of
objects including medical devices by irradiation by gas-cluster
ion-beam (GCIB). The sterilization may be performed in combination
with other GCIB processing of the object.
BACKGROUND OF THE INVENTION
[0003] Sterilization of objects such as medical devices or
surgically implantable devices or prostheses has traditionally been
done by a variety of methods including steam or dry heating,
ultraviolet, x-ray, or gamma-ray irradiation, plasma sterilization,
conventional ion beam irradiatiation, and exposure to sterilant
gases or germicidal fluids.
[0004] Gas-cluster ions are formed from large numbers of weakly
bound atoms or molecules sharing common electrical charges and they
can be accelerated to have high total energies. Gas-cluster ions
disintegrate upon impact and the total energy of the cluster ion is
shared among the constituent atoms. Because of this energy sharing,
the atoms are individually much less energetic than in the case of
un-clustered conventional ions and, as a result, the atoms only
penetrate to much shallower depths than would conventional ions.
Surface effects can be orders of magnitude stronger than
corresponding effects produced by conventional ions, thereby making
important micro-scale surface modification effects possible that
are not possible in any other way.
[0005] The concept of gas-cluster ion-beam (GCIB) processing has
only emerged in recent decades. Using a GCIB for dry etching,
cleaning, and smoothing of materials, as well as for film formation
is known in the art and has been described, for example, by
Deguchi, et al. in U.S. Pat. No. 5,814,194, "Substrate Surface
Treatment Method", 1998. Because ionized gas-clusters containing on
the order of thousands of gas atoms or molecules may be formed and
accelerated to modest energies on the order of a few thousands of
electron volts, individual atoms or molecules in the clusters may
each only have an average energy on the order of a few electron
volts. It is known from the teachings of Yamada in, for example,
U.S. Pat. No. 5,459,326, that such individual atoms are not
energetic enough to significantly penetrate a surface to cause the
residual sub-surface damage typically associated with plasma
polishing or conventional monomer ion beam processing.
Nevertheless, the clusters themselves are sufficiently energetic
(some thousands of electron volts) to effectively etch, smooth, or
clean hard surfaces, or to perform other shallow surface
modifications.
[0006] Because the energies of individual atoms within a
gas-cluster ion are very small, typically a few eV, the atoms
penetrate through only a few atomic layers, at most, of a target
surface during impact. This shallow penetration of the impacting
atoms means all of the energy carried by an entire cluster ion is
consequently dissipated in an extremely small volume in the top
surface layer during an extremely short time interval. This is
different from the case of ion implantation, which is normally done
with conventional ions and where the intent is to penetrate into
the material, sometimes penetrating several thousand angstroms, to
produce changes in both the surface and sub-surface properties of
the material. Because of the high total energy of the cluster ion
and extremely small interaction volume of each cluster, the
deposited energy density at the impact site is far greater than in
the case of bombardment by conventional ions and the extreme
conditions permit material modifications not otherwise
achievable.
[0007] Irradiation by GCIB has been successfully applied in a
variety of surface modification processes including cleaning,
smoothing, surface infusion, deposition, etching, and changing
surface characteristics such as making a surface more or less
wettable. The cleaning, smoothing, etching, and wettability
modification processes (for example) are sometimes useful for
improving the surfaces of medical devices, surgical implants, and
medical prostheses. It is desirable and necessary that many types
of medical devices, implants, and prostheses be sterile for use in
their intended applications.
[0008] It is therefore an object of this invention to provide
methods and apparatus for surface sterilization of objects
including medical devices, surgical implants, and/or medical
prostheses by GCIB irradiation.
[0009] It is another object of this invention to provide methods
and apparatus for multi-step processing of objects including a step
of surface sterilization by GCIB irradiation in combination with
another GCIB surface processing step on the same object.
[0010] It is a further object of this invention to provide methods
and apparatus for surface sterilization of objects, without
significantly elevating the temperature of the bulk of the object
and without the use of toxic materials.
SUMMARY OF THE INVENTION
[0011] The objects set forth above, as well as further and other
objects and advantages of the present invention, are achieved as
described hereinbelow.
[0012] One embodiment of the present invention provides method for
sterilizing a workpiece, comprising the steps of: providing a
reduced pressure chamber; forming an accelerated gas-cluster
ion-beam having a path in the reduced pressure chamber; providing a
workpiece holder in the reduced pressure chamber for holding the
workpiece in the accelerated gas-cluster ion-beam path; and
irradiating at least a portion of a surface of the workpiece with
the accelerated gas-cluster ion-beam for sterilizing the
portion.
[0013] The irradiating step may introduce a dose of at least
10.sup.13 ions/cm.sup.2 to the at least a portion of the surface of
the workpiece. The forming step may include accelerating the
gas-cluster ion-beam using an acceleration potential of at least 2
kV. The forming step may comprise forming a gas-cluster ion-beam
comprising a noble gas or a mixture of a noble gas with oxygen. The
at least a portion of a surface may be an entire surface. The step
of providing a workpiece holder may further comprise sterilizing
the workpiece holder.
[0014] Another embodiment of the present invention provides a
method for sterilizing a workpiece, comprising the steps of: a.
providing a chamber having an interior and a workpiece holder in
the interior; b. initially sterilizing the workpiece holder and the
interior of the chamber; c. forming an accelerated gas-cluster
ion-beam; d. loading a workpiece onto the workpiece holder to be
held thereby for sterilization; e. reducing the pressure in the
chamber; f. directing the accelerated gas-cluster ion-beam onto the
workpiece; g. irradiating at least a portion of a surface of the
workpiece with the accelerated gas-cluster ion-beam; h.
discontinuing irradiation when the at least a portion of a surface
of the workpiece has received a predetermined dose; and i.
unloading the workpiece from the workpiece holder and removing it
from the chamber.
[0015] The method may further comprise the step of venting the
chamber with a sterile gas. The method may further comprise the
step of: repeating steps d. through i. at least once. The at least
a portion of a surface may be an entire surface. The step of
unloading may include placing the workpiece directly into a sterile
container.
[0016] Yet another embodiment of the present invention provides a
method for sterilizing a workpiece, comprising the steps of:
providing a chamber having an interior and a workpiece holder;
initially sterilizing the workpiece holder and the interior of the
chamber; loading a workpiece onto the workpiece holder to be held
thereby; forming a first accelerated gas-cluster ion-beam;
directing the first accelerated gas-cluster ion-beam onto the
workpiece; first processing the workpiece by irradiating at least a
first portion of the surface of the workpiece with the first
accelerated gas-cluster ion-beam; discontinuing first processing
when the at least a first portion of the surface of the workpiece
has received a predetermined dose; forming a second accelerated
gas-cluster ion-beam; directing the second accelerated gas-cluster
ion-beam onto the workpiece; second processing the workpiece by
irradiating at least a second portion of the surface of the
workpiece with the second accelerated gas-cluster ion-beam;
discontinuing second processing when the at least a second portion
of the surface of the workpiece has received a predetermined dose;
unloading the workpiece from the workpiece holder and removing it
from the chamber; and wherein either of the first processing step
or the second processing step is a sterilizing step. The at least a
first portion of the surface and the at least a second portion of
the surface may be the same portion of the surface.
[0017] Still another embodiment of the present invention provides
apparatus for sterilizing a workpiece, comprising: a reduced
pressure chamber having an interior; a sterilizer adapted for
initially sterilizing the interior of the reduced pressure chamber;
an apparatus adapted for forming an accelerated gas-cluster
ion-beam having a path in the interior of the reduced pressure
chamber; a workpiece holder adapted for holding a workpiece in the
path of the accelerated gas-cluster ion-beam in the interior of the
reduced pressure chamber for receiving an irradiated gas-cluster
ion-beam dose on at least a portion of the surface of the
workpiece; a vent adapted for venting the reduced pressure chamber
with a sterile gas; and a mechanism adapted for loading and/or
unloading the workpiece onto or off of the holding means in the
reduced pressure chamber and adapted for introducing and/or
removing the workpiece from the reduced pressure chamber.
[0018] The workpiece holder may further comprise means for
rotating, articulating, repositioning, or moving the workpiece to
provide for receiving an irradiated gas-cluster ion-beam dose on
multiple portions of the surface of the workpiece. The multiple
portions of the surface the workpiece may comprise the entire
surface of the workpiece.
[0019] The apparatus adapted for forming an accelerated gas-cluster
ion-beam may further comprise: a nozzle; a skimmer; an ionizer; and
an accelerator. The apparatus may further comprising a device
adapted for scanning the accelerated gas-cluster ion-beam.
[0020] The sterilizer adapted for initially sterilizing the
interior of the reduced pressure chamber may comprise means for
introducing and removing a sterilant gas to/from the interior of
the reduced pressure chamber. The sterilizer adapted for initially
sterilizing the interior of the reduced pressure chamber may
comprise means for irradiating the interior of the reduced pressure
chamber with ultraviolet radiation.
[0021] For a better understanding of the present invention,
together with other and further objects thereof, reference is made
to the accompanying drawings and detailed description and in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a is a schematic view of a GCIB processing system
of the present invention;
[0023] FIG. 2 is an enlarged view of a portion of the GCIB
processing system, showing the workpiece holder and manipulator for
handling the object to be sterilized;
[0024] FIG. 3 is a schematic of a sterilizing system for GCIB
sterilization of workpieces;
[0025] FIG. 4A is a photograph of a control titanium foil showing
bacterial colonies growing thereon;
[0026] FIG. 4B is a photograph of a conventionally sterilized
titanium foil showing no bacterial colonies growing thereon;
and
[0027] FIG. 4C is a photograph of a GCIB irradiated titanium foil
showing no bacterial colonies growing thereon, indicating
effectiveness of GCIB sterilization.
DETAILED DESCRIPTION OF THE PREFERRED METHODS AND EMBODIMENTS
[0028] In the following description, for simplification of the
drawings, item numbers from earlier figures may appear in
subsequent figures without discussion. In such cases items with
like numbers are like items and have the previously described
features and functions.
[0029] FIG. 1 shows an embodiment of the (GCIB) processor 100 of
this invention utilized for the surface sterilization of a
workpiece 10 (which may be a medical device, surgical implant, or
medical prosthesis or some other sterilizable object). Although not
limited to the specific components described herein, the GCIB
processor 100 is made up of a vacuum vessel 102 which is divided
into three communicating chambers, a source chamber 104, an
ionization/acceleration chamber 106, and a process chamber 108
which includes therein a uniquely designed workpiece holder 150
capable of positioning the medical device for uniform processing by
a gas-cluster ion-beam.
[0030] During the processing method of this invention, the three
chambers are evacuated to suitable operating pressures by vacuum
pumping systems 146a, 146b, and 146c, respectively. A condensable
source gas 112 (for example argon, O.sub.2, etc.) stored in a
cylinder 111 is admitted under pressure through gas metering valve
113 and gas feed tube 114 into stagnation chamber 116 and is
ejected into the substantially lower pressure vacuum through a
properly shaped nozzle 110, resulting in a supersonic gas jet 118.
Cooling, which results from the expansion of the jet, causes a
portion of the gas jet 118 to condense into clusters, each
consisting of from several to several thousand weakly bound atoms
or molecules, and typically having a distribution having a most
likely size of hundreds to thousands of atoms or molecules. A gas
skimmer aperture 120 partially separates the gas molecules that
have not condensed into a cluster jet from the cluster jet so as to
minimize pressure in the downstream regions where such higher
pressures would be detrimental (e.g., ionizer 122, high voltage
electrodes 126, and process chamber 108). Suitable condensable
source gases 112 include, but are not necessarily limited to argon
or other noble gases, oxygen, oxygen-containing gases, other
reactive gases, and mixtures of these or other gases.
[0031] After the supersonic gas jet 118 containing gas clusters has
been formed, the clusters are ionized in an ionizer 122. The
ionizer 122 is typically an electron impact ionizer that produces
thermoelectrons from one or more incandescent filament(s) 124 and
accelerates and directs the electrons causing them to collide with
the gas clusters in the gas jet 118, where the jet passes through
the ionizer 122. The electron impact ejects electrons from the
clusters, causing a portion the clusters to become positively
ionized. A set of suitably biased high voltage electrodes 126
extracts the cluster ions from the ionizer 122, forming a beam,
then accelerates the cluster ions to a desired energy (typically
using an acceleration potential of from about 2 keV to as much as
100 keV) and focuses them to form a GCIB 128 having an initial
trajectory 154. Filament power supply 136 provides voltage V.sub.F
to heat the ionizer filament 124. Anode power supply 134 provides
voltage V.sub.A to accelerate thermoelectrons emitted from filament
124 to cause them to bombard the cluster containing gas jet 118 to
produce ions. Extraction power supply 138 provides voltage V.sub.E
to bias a high voltage electrode to extract ions from the ionizing
region of ionizer 122 and to form a GCIB 128. Accelerator power
supply 140 provides voltage V.sub.Acc to bias a high voltage
electrode with respect to the ionizer 122 so as to result in a
total GCIB acceleration potential equal to V.sub.Acc volts. One or
more lens power supplies (142 and 144, for example) may be provided
to bias high voltage electrodes with potentials (V.sub.L1 and
V.sub.L2, for example) to focus the GCIB 128.
[0032] Referring now to FIG. 2, a workpiece 10 to be processed by
GCIB irradiation using the GCIB processor 100 is/are held on a
workpiece holder 150, disposed in the path of the GCIB 128. In
order to facilitate uniform processing of one or more surfaces or
surface regions of the workpiece 10, the workpiece holder 150 is
designed in a manner set forth below to position and/or manipulate
the workpiece 10 to expose multiple surface regions for GCIB
processing.
[0033] As will be explained further hereinbelow, the practice of
the present invention is facilitated by an ability to control
positioning of the object to be sterilized with respect to the GCIB
is required to assure irradiation of all necessary surfaces of the
object being sterilized. Objects being sterilized may have multiple
surfaces with different surface orientations. It is desirable that
there be a capability for positioning and orientating the object to
be sterilized with respect to the GCIB. This requires a fixture or
workpiece holder 150 with the ability to be fully articulated in
order to orient all desired surfaces of a workpiece 10 to be
sterilized, within the GCIB to assure incidence for the desired
surface irradiation effect. More specifically, when processing a
workpiece 10, the workpiece holder 150 is rotated and articulated
by an articulation/rotation mechanism 152 located at the end of the
GCIB processor 100.
[0034] Referring again to FIG. 1, the articulation/rotation
mechanism 152 preferably permits 360 degrees of device rotation
about longitudinal axis coinciding with the trajectory 154 and
sufficient device articulation about an axis 157 that may be
perpendicular to the longitudinal axis coinciding with the
trajectory 154 to expose the objects surfaces to the GCIB for
irradiation. Under certain conditions, depending upon the size of
the workpiece 10, which is to be sterilized, a scanning system may
be desirable to produce uniform irradiation of the medical device
with the GCIB 128. Although not necessary for all GCIB processing,
two pairs of orthogonally oriented electrostatic scan plates 130
and 132 may be utilized to produce a raster or other beam scanning
pattern over an extended processing area. When such beam scanning
is performed, a scan generator 156 provides X-axis and Y-axis
scanning signal voltages to the pairs of scan plates 130 and 132
through lead pairs 158 and 160 respectively. The scanning signal
voltages may be triangular waves of different frequencies that
cause the GCIB 128 to be converted into a scanned GCIB 148, which
scans an entire surface or extended region of the workpiece 10. As
an alternative to scanning the GCIB across the workpiece 10, the
workpiece holder 150 may be designed to move the medical device
through a stationary GCIB in a scanning motion relative to the
GCIB.
[0035] When beam scanning over an extended region is not desired,
processing is generally confined to a region that is defined by the
diameter of the beam. The diameter of the beam at the surface of
the workpiece 10 can be set by selecting the voltages (V.sub.L1
and/or V.sub.L2) of one or more lens power supplies (142 and 144
shown for example) to provide the desired beam diameter at the
workpiece.
[0036] Gas-cluster ion-beam processing is used in semiconductor
processing and fabrication as a technology that provides extreme
processing accuracy A further advantage to GCIB sterilization over
other radiation techniques is the unique ability to process only
the exposed surface while not having any effect on the sub-surface
regions of the product. GCIB does not significantly penetrate nor
permeate the object being sterilized and has no effect on the bulk
portion of the object
[0037] The GCIB process can be described as follows. First, the
device to be sterilized is placed into a vacuum vessel mounted on
suitable fixtures to allow the device to be manipulated so that all
surface areas can be exposed to the GCIB beam during processing.
Second, the vessel is pumped to high vacuum condition, ideally at
lower than 1.3.times.10.sup.-2 pascal pressure vacuum. Once
process-level vacuum is attained in the vacuum vessel, a gate valve
is opened between the processing vacuum vessel and the main GCIB
tool. The gas-cluster ion-beam is then allowed to expose all
surfaces of the substrate to gas-cluster ion bombardment to an
exposure equal to or greater than 10.sup.13 ions per square
centimeter, a level sufficient to assure cluster ion impact upon
every biologically active organism. The gas clusters are typically
formed from gases such as, but are not necessarily limited to argon
or other noble gases, oxygen, oxygen-containing gases, other
reactive gases, and mixtures of these or other gases.
[0038] Once the clusters are generated and formed into a beam,
applying a high voltage accelerating potential of from 5 to 200 kV
accelerates them. This high voltage potential accelerates the
gas-cluster ions toward the substrate and thereby causes the
clusters to impact the surface to be sterilized, releasing all
their energy into that surface. The impact and energy release at
the point of each cluster impact causes an intense thermal spike
exceeding 1000 degrees Kelvin, but of extremely short duration, to
occur only in the immediate localized region, typically in the
topmost 100 angstroms only. Without wishing to be bound by a
specific theory, it is believed that it may be this enormous
temperature spike occurring only at the surface that destroys all
biological contaminants. The high vacuum system pumps away all
volatile organics and maintains a contaminant free surface state
while processing continues. When the entire surface has been
bombarded at the desired dose, the irradiation is terminated. The
sterilized piece is now maintained in a high-vacuum
contaminant-free state until the vacuum system is closed off and
the vessel is returned to atmosphere by backfilling with an inert,
sterile gas.
[0039] FIG. 3 is a schematic of a sterilizing system 300
specifically adapted according to the invention for GCIB
sterilization processes. The vacuum vessel 102 includes a process
chamber 108 that can be isolated from the GCIB source by an
isolation valve 302. Isolation valve 302 has open and closed
states. In the open state, isolation valve 302 permits a GCIB 128
to enter the process chamber 108 for irradiating a workpiece 10 to
be sterilized while held by a workpiece holder 150. The workpiece
holder 150 may be designed as previously described (during
discussion of FIGS. 1 and 2 above) to rotate and/or articulate the
workpiece 10 by means of articulation/rotation mechanism 152, or it
may have other designs for fixedly supporting or for manipulating
the workpiece 10, as will be readily apparent to those skilled in
the art, for exposing single or multiple surfaces of the workpiece
to the GCIB 128 (as may be required by the geometry of the
workpiece and the sterilization requirements.) In the closed state,
isolation valve 302 isolates the process chamber 108 from the GCIB
source. The GCIB source may be similar to that shown in FIG. 1, or
may be some other conventional GCIB source. The GCIB 128 provided
by the GCIB source may be a scanned or an un-scanned GCIB as may be
suitable for the size of the workpiece 10 to be sterilized.
[0040] A vacuum system 306 is coupled to the process chamber 108 by
an isolation valve 304. Isolation valve 304 has open and closed
states and may be manually or automatically controlled. When in the
open state, isolation valve 304 permits evacuation of the process
chamber 108 by the vacuum system 306. When in the closed state,
isolation valve 304 inhibits evacuation of the process chamber 108
and permits the introduction of non-vacuum atmospheres to the
process chamber 108. A vent line 310 has a valve 312 for
controlling introduction of a sterile venting gas 308 to the
process chamber 108. A sterilant gas 320 may optionally be
introduced to the process chamber 108 through valve 318 for initial
sterilization of the process chamber 108 and workpiece holder 150
or for re-sterilization after a contamination event. An optional
radiation source 322, which may be a short-wave ultraviolet
radiation source may also be used for initial sterilization of the
process chamber 108 and workpiece holder 150 or for
re-sterilization after a contamination event. When an ultraviolet
radiation source is used, the interior of the process chamber 108
may contain considerable reflective metal to reflect the
ultraviolet radiation throughout the interior of the process
chamber 108.
[0041] A loading/unloading/packaging environment 316 is coupled to
the process chamber 108 by an isolation valve 314. Isolation valve
314 has an open state and a closed state. When isolation valve 314
is open, workpieces to be sterilized may be moved from the
loading/unloading/packaging environment 316 to the workpiece holder
150 for GCIB sterilization. Likewise, sterilized workpieces can be
moved from the workpiece holder 150 to the
loading/unloading/packaging environment 316 for sterile packaging
before removal from the sterilizing system 300. Conventional
mechanisms and/or robotic handlers may perform the transfers and
packaging of the workpiece.
[0042] In typical operation, the process chamber 108 of the
sterilizing system 300 is initially cleaned and then initially
sterilized. Initial sterilization of the process chamber 108, and
mechanisms therein including the workpiece holder 150 may be done
by evacuating process chamber 108, then closing the valves 304,
312, 302, and 314 and introducing a sterilant gas 320 to the
process chamber through valve 318. After allowing adequate time for
sterilization, the valve 318 may be closed and the sterilant gas
evacuated from the process chamber 108 by opening isolation valve
304 and evacuating the process chamber 108 using vacuum system 306.
Alternatively, the interior of the process chamber 108 and
mechanisms contained therein including the workpiece holder 150 may
be initially sterilized by closing valves 312, 302, 318, and 314
and evacuating the process chamber 108 through isolation valve 304
using vacuum system 306--then by activating radiation source 322,
which may be a short-wave ultraviolet radiation source, to
sterilize the process chamber 108 and mechanisms therein.
[0043] After initial sterilization of the process chamber 108, one
or more workpiece(s) 10 to be sterilized may be loaded sequentially
or in parallel onto the workpiece holder 150, evacuated, and
irradiated by GCIB 128. The process chamber 108 may then be vented
to atmospheric pressure using a sterile venting gas 308, and the
workpiece 10 then unloaded to the loading/unloading/packaging
environment 316 for packaging and/or removal from the sterilizing
system 300. The loading/unloading/packaging environment 316 may
enable direct insertion of sterilized work pieces into sterile
containers. The load-sterilize-unload cycle may be repeated as many
times as required for the sterilization job at hand.
[0044] The workpiece 10 is not exposed to sterilant gas 320 nor to
radiation source 322, but rather is only sterilized by GCIB 128,
avoiding exposure to toxic materials and/or undesirable effects of
radiation or other sterilizing methods. The sterilization that is
performed via the present invention may also be limited to certain
areas to further prevent any adverse affects on the finished
product from this very process.
[0045] Gas-cluster ion-beam processing may be used to perform
in-situ or post-process sterilization of medical devices with
specific sterilization process needs. Certain situations where
other known sterilization techniques such as UV light, high
temperature exposure, or wet method processing are not suitable can
benefit from use of this new alternative method. Surface-only
processing makes this technology attractive when compared to other
methods that may cause product damage or create unwanted
degradation by damaging the subsurface regions that are not a
source of bio-contamination. GCIB sterilization (as a final in-situ
step), in combination with other GCIB surface processing step(s),
in particular GCIB-induced or GCIB-assisted drug deposition
application steps, GCIB etching steps, GCIB smoothing steps, etc.,
make this technology particularly useful and advantageous. In such
applications, the initially sterilized process chamber 108 is
loaded with the workpiece 10, multiple GCIB processing steps
including a GCIB sterilizing step are preformed, and the finished
product removed and optionally packaged.
[0046] Specific applications of the present invention include drug
eluting implants and implants having areas adapted for enhanced
cell growth. Drug eluting implants, such as stents, which finely
control the area of coated drugs can be created using the present
invention. Implants with areas adapted for enhanced cell growth
using GCIB can be sterilized as part of the GCIB process to further
reduce any risk of contamination.
[0047] The advantages of using GCIB processing are numerous and can
be generalized as follows: First, the processing is carried out in
a vacuum environment which provides complete environmental control
over biological contamination and provides safe storage until the
packaging process can begin. Second, the GCIB process affects only
a shallow surface layer, leaving the underlying material undamaged
and creating no sub-surface damage or degradation. Third, GCIB
allows extreme heat sterilization of the immediate surface without
significantly heating the bulk material, thus allowing
sterilization of temperature-sensitive materials at approximately
ordinary room temperatures. Another benefit of GCIB sterilization
is the avoidance of ultraviolet, x-ray, or gamma ray, or other
types of damage caused by other conventional techniques that can
cause degradation of many materials. The combination or individual
merits of these advantages may make GCIB sterilization attractive
for situations that cannot tolerate wet processing, ultraviolet
exposure or oxidative environments or situations where
environmental control is difficult prior to packaging.
[0048] While GCIB has advantages in many applications, there are
also limitations that must be considered before choosing GCIB
sterilization processing. First, the product for sterilization must
be vacuum compatible. This means that the product must be able to
withstand the rigors of the vacuum process without damage, and that
the product is compatible with a vacuum level suitable for GCIB
processing. Further, it is important that this vacuum level can be
maintained while processing without excessive product out-gassing
that may adversely affect the GCIB process. Lastly, GCIB is a "line
of sight" process, which means that all surfaces of the sample that
are intended to be sterilized must be exposed to the beam for the
process to work. Depending on the shape and complexity of the
object being sterilized, this may require very elaborate fixtures
and manipulation tools and may prove to be impractical or
impossible for some complex shapes. For many shapes and geometries,
the required multiple exposures can be readily accomplished by
manipulating, rotating, articulating, and/or repositioning the
object during processing using conventional holding mechanisms that
will be readily known by those skilled in the art.
Exemplary Embodiment
[0049] Titanium was selected as an exemplary substrate for
evaluation of GCIB sterilization since titanium is one of several
commonly employed materials for implantable medical devices and
prostheses. Titanium foil was cut into pieces of approximately 1.5
cm.times.1.5 cm square. The cut pieces of titanium foil were openly
exposed to ambient atmosphere in an inhabited area for 24 hours to
promote the incidence of bacteria and/or bacterial spores to attach
to the surface of the titanium foil squares. Following ambient
exposure, Group 1 of the titanium foil squares was treated with
argon GCIB irradiation at 30 kV acceleration potential with
5.times.10.sup.14 ions/cm.sup.2 dose on both sides, for a total
GCIB irradiation time of 90 seconds. Following ambient exposure,
Group 2 was sterilized using a conventional sterilization process
by being placed in a sterilization pouch and subjected to 20
minutes in a Harvey.RTM. Chemiclave 5000 sterilizer with
Harvey.RTM. Vapo-Sterile solution. As a control, Group 3 was not
further treated after the exposure to ambient atmosphere. Foil from
each group was placed in individual pre-warmed LB-Agar (Luria
Bertani Agar, a general purpose, non preferential, bacterial
culture medium) plates (Sigma L5542) and placed in a 37.degree. C.
incubator for 72 hours and bacterial colonies were visually
quantified.
[0050] FIG. 4A shows a photograph 400A of a Group 3 (control group)
titanium foil piece 402 in agar medium 404 showing the presence of
numerous bacterial colonies growing on the foil several exemplary
bacterial colonies 406 are indicated on the photograph.
[0051] FIG. 4B shows a photograph 400B of a Group 2 (conventionally
sterilized) titanium foil piece in agar medium showing complete
absence of bacterial colonies, indicating sterilization after
ambient exposure.
[0052] FIG. 4C shows a photograph 400C of a Group 1 (GCIB
sterilized) titanium foil piece in agar medium, again showing
complete absence of bacterial colonies, indicating the
effectiveness of the GCIB sterilization after ambient exposure.
[0053] Both Groups 1 and 2 had no bacterial colonies present,
representing 0% surface area occupied by colonies. In comparison,
the untreated control Group 3 had 27 visible bacterial colonies,
several of which may have been the product of multiple colonies
merging into a larger colony. All of the control Group 3 samples
had visible bacterial colonies. None of the Group 1 or Group 2
samples had visible bacterial colonies. The total titanium surface
covered by bacterial colonies for the control Group 3 was about
15%.
[0054] Although the invention has been described with respect to
various embodiments, it should be realized this invention is also
capable of a wide variety of further and other embodiments within
the spirit and scope of the invention and the appended claims.
* * * * *